Chapter 1
The Development of Lasers

Photo by: ann triling

A laser is a device that produces an unusually powerful beam of light that
does not exist on its own in nature. Today this light is used to perform
thousands of useful tasks. A laser can give off a light beam that blasts
through a thick metal wall or bores a hole in a diamond. Some lasers can
measure things seen only under a microscope or even perform delicate eye
operations. Every day, lasers are used in communications, factories,
hospitals, and various entertainment media. In fact, lasers make our lives
better and easier in so many ways that scientists have come to refer to
these devices as the supertools of the modern age.

The invention of the laser was the result of many ideas and discoveries,
each building upon the ones that came before it, going back more than a
hundred years. Scientists did not purposely set out to invent the laser;
in fact, no one seriously considered such a device until just a few years
before the first laser was built. Most of the ideas that led to its
invention were the results of attempts by scientists to learn more about
light and how it behaves. As time went on, the idea that light might be
made more powerful, or amplified, became more important to scientists.
Only when a few researchers managed to put all these accumulated ideas
together in a very special way did it occur to them that something like a
laser could be built.

The Photophone and Early Theories of Light

The first important attempt to get light to perform a task that lasers
perform today came in the year 1880. Noted American inventor Alexander
Graham Bell performed an experiment that showed how light might be used to
carry a person's voice from one location to another. To accomplish
this, Bell used a device he called a photophone, which consisted of a thin
mirror, a receiver that could detect light, some wires, and an earpiece.
Bell placed the mirror so that sunlight reflected off of its surface and
traveled more than one hundred feet to the receiver. When a person spoke
near the delicate mirror, it vibrated slightly. This caused the sunlight
being reflected into the receiver to vibrate, too. The receiver then
changed the light vibrations into an electrical signal, which traveled
through the wires to the earpiece.

A man demonstrates Alexander Graham Bell's photophone, a
crude but ingenious attempt to make light transmit a human voice.

Unfortunately the photophone did not work very well. Bell's
receiver was very crude compared to the ones used today. Also, the device
relied on sunlight, which varies in brightness from hour to hour and from
day to day. Obviously, on cloudy days or at night the device could not be
used at all. Bell also had to contend with the fact that scientists at
that time still did not know enough about light in order to use its power.
What they did know was that light always travels at a set speed, which
happens to be about 186,000 miles (300,000 kilometers) per second. This is
so fast that a beam of light can race around the earth almost seven and a
half times in a second.

But in order to use light as a tool it was not enough to know how fast
light travels. People also needed to know what light is made of. Back in
the 1600s English scientist Sir Isaac Newton had suggested that light was
made up of tiny particles. This explanation became known as the particle
theory of light. At about the same time, Dutch scientist Christian Huygens
said that light might be composed of waves, similar to the ocean waves
that roll onto a beach. Scientists dubbed this the wave theory of light.

Unfortunately, in Bell's day scientists still argued over which of
these theories was correct. Through a mixture of hard work and genius,
however, Bell managed to build a working photophone. The device itself
operated on principles different from those that would later be used in
the laser. Yet Bell had demonstrated that light might someday be used in
communications. This idea prepared the way for the next step toward the
discovery of the laser.

Einstein and Stimulated Light

In 1905 German scientist Albert Einstein announced his own theory about
light, namely that it is made up of both particles
and
waves. Einstein claimed that the particles, called photons (from the
Greek word for "light"), move along in wavelike patterns.
Later, other scientists
performed experiments that proved Einstein was right. Einstein himself
then went on to predict some more startling things about light, first and
foremost how photons are made. He agreed with some other scientists of his
day about how light sources (like candles, light bulbs, or the sun)
produce photons. The researchers thought that atoms (the tiny particles
that make up all material in the universe) give off photons. Some form of
energy—such as heat, electricity, or chemical energy—might
"excite" an atom, or make it more energetic. It would then
emit (give off) a photon. Afterward, the atom would go back to its normal,
unexcited state. Because there are huge numbers of atoms, they give off
equally large numbers of photons. A 100-watt light bulb gives off about 10
trillion photons every second.

Physicist Albert Einstein suggested the concept of the stimulated,
or amplified, emission of light.

In 1917 Einstein suggested that while an atom is excited it might be
stimulated (coaxed) to produce a photon. If enough atoms could be excited
and stimulated, a great number of photons might be produced. A beam of
light made up of so many photons would be highly concentrated and
therefore brighter and more powerful. Einstein called this process
"stimulated emission of light." Because it can produce light
that is boosted in power, or amplified, stimulated emission is the basic
principle of laser operation.

Scientists had the basic information they needed to build a laserlike
device as early as 1917. But no one actually attempted it. Researchers
thought it would be too difficult and expensive; and they were right. The
advanced machinery they needed did not exist at the time and would have to
be developed piece by piece. The necessary research would take many years
and cost a lot of money. Of course, such time and money
would be worthwhile if the idea promised to be useful enough. But the
vast majority of scientists at that time did not think the idea of
amplifying light would lead to anything practical or useful. For this
reason, the development of lasers occurred in a more roundabout
way—through experiments with radar and microwaves.

Radar and Microwaves

During World War II (1939–1945) scientists worked hard at improving
radar, a tracking device that had been invented a few years earlier. Radar
sends out a beam of microwaves that bounces off nearby objects. Microwaves
are similar to visible light, as both travel at 186,000 miles per second
and are made up of particles that move

A naval technician tests radar equipment in August 1945. Experiments
with radar led to technical advances that eventually produced the
laser.

in waves. But unlike light, which people can see, microwaves are
invisible to the eye. After a radar beam bounces off an object the
reflected microwaves return and register on a screen. By studying the
screen a radar operator can tell the general size and distance of the
object. This is how soldiers located enemy airplanes during World War II.

As the war dragged on American military scientists tried to find ways of
producing more powerful microwaves. Led by Dr. Charles Townes, these
researchers found that microwave radiation does not work very well for
radar because the waves are too easily absorbed by water vapor in the air;
and as the beam travels farther more of it gets absorbed, so it gets too
weak to do any good. But in a way, these experiments had not failed. They
had made Townes very interested in learning more about microwaves,
research that would eventually lead to the laser.

In 1947 Townes began teaching and doing research at Columbia University in
New York City. He remembered what Einstein had said about the stimulated
emission of visible light—that many atoms could be stimulated to
produce many particles of light. Since microwaves are so similar to light,
Townes reasoned that stimulation might also produce many microwave
particles. If the microwaves could be produced by stimulation, perhaps
enough of them could be built up to get an amplified beam. But what would
be the purpose of such a beam? Townes was not sure it would have any
practical uses, but he reasoned it would be an effective research tool to
aid scientists in studying how atoms give off radiation.

The Maser—Precursor of the Laser

In 1951, while sitting on a park bench, Townes had a brilliant idea. He
realized it might be possible to use molecules of ammonia to produce a
powerful microwave beam. (A molecule consists of two or more atoms that
are connected together.) Townes reasoned

that when molecules of ammonia became excited (by heat, electricity, or
chemical energy), they could be stimulated to emit microwaves of the type
he was working with. He knew this process would be almost identical to the
one Einstein described for stimulating visible light. The only difference
was that Townes would be using microwaves instead of light. He calculated
that if the ammonia molecules could be kept in an excited state long
enough, they might be stimulated to produce more and more microwaves.
Eventually, the waves would become concentrated and more powerful. In
short, the microwaves would be amplified.

Townes decided to try to build a working model. He enlisted the aid of two
other researchers, Herbert J. Zigler and James P. Gordon. Working
diligently, by 1954 the three men had a working device that operated
in the following way: First, some ammonia gas was heated until many of
the molecules became excited and then were separated from the unexcited
molecules. Next, the excited molecules flowed into a chamber called the
resonant cavity (or resonator) where the stimulation of the molecules took
place. As the excited ammonia molecules began to emit microwave particles,
the particles began to bounce back and forth inside the chamber. When one
of these particles came near an excited molecule, the molecule suddenly
gave off its own particle. Thus the particles themselves stimulated the
production of more particles. Soon the number of particles doubled, then
doubled again and again until the microwaves in the chamber had become
very powerful.

The entire process took only a tiny fraction of a second. Out of a hole in
the resonator shot a strongly amplified beam of microwaves. The scientists
called their invention a maser. The letters of this acronym stand for
m
icrowave
a
mplification by
s
timulated
e
missions of
r
adiation. The ammonia maser had only a few practical uses. First, because
the ammonia molecules in the maser vibrated at a steady rate, the device
could be used as a reliable timekeeping device. Second, because the maser
was an amplifier, it could boost the weak microwave signals given off by
distant stars, making it easier for astronomers to study such signals and
learn more about stars.

Initial Laser Concepts and Designs

Townes and other researchers did not know it then, but the most important
thing about the maser was that it set the stage for the development of the
laser. All the right ingredients needed for the laser had been combined in
the maser except for the most important one—light. In the
mid-1950s, soon after the introduction of the maser, some researchers
began talking about a device that would stimulate atoms to emit photons of
light, exactly as Einstein had described. The photons
would then be amplified to produce a powerful beam of light.

How a Maser Works

A maser amplifies, or increases, the number of photons that cause
invisible electromagnetic waves known as microwaves. First, heated
ammonia gas is pumped into the maser. There, "unexcited,"
or low-energy, molecules are drawn to the sides of the maser. Only
"excited," or high-energy, ammonia molecules flow into the
resonator, or vibrating chamber. In this chamber, the excited molecules
begin to emit microwave photons. These photons bounce around in the
resonator, striking the ammonia molecules so that they remain excited
and produce more and more microwaves.

One researcher who wanted to learn how to amplify light was the father of
the maser, Charles Townes. In September 1957 Townes drew a design for a
device he called an "optical maser" (the term
laser
not yet having been coined). He then called another scientist, Arthur
Schawlow, and the two men began drawing up more detailed plans for the
optical maser. Townes and Schawlow were not the only ones working
on the laser idea, however. Nikolai Basov and Aleksandr Prokhorov in the
Soviet Union were also exploring the idea, and Gordon Gould, a graduate
student at Columbia University, was thinking about developing his own
light-amplifying device.

In November 1957, only two months after Townes had sketched the optical
maser design, Gould wrote down in notebooks all his ideas for his own
proposed invention. The first thing he wrote was a name for the device. He
called it a laser, which stood for
l
ight
a
mplification by
s
timulated
e
mission of
r
adiation. Other researchers thought of this name on their own, but
apparently Gould was the first to coin the term.

Hearing that Towne might also be working on lasers, Gould got worried.
Naturally, he did not want someone else to get credit for what he
considered to be his own invention. He showed his notes to a lawyer who
specialized in patents. (When the government grants a person a patent for
an invention, it recognizes that person as the original inventor. The
person who holds the patent can also make a lot of money if the invention
is successful.) Unfortunately for Gould, the lawyer did not understand the
information in the notebooks and gave Gould the mistaken idea that he
needed a working model of his invention in order to get a patent.

Gould was not sure what to do next, so he just waited. This turned out to
be a mistake because in the meantime Townes and Schawlow had been hard at
work. They applied for their own patent in the summer of 1958. They also
wrote a paper explaining their ideas and had it published in a famous
science magazine. Gould had not published a paper; and when he finally did
apply for a patent, almost a year had elapsed since Townes and Schawlow
had obtained their own patent. So no one believed Gould later when he
claimed he had come up with the idea for lasers on his own.

Building the First Laser

By 1960 many scientists, including Townes and Schawlow, Basov and
Prokhorov, and Gould, had asked for laser patents. In addition, the paper
published by Townes and Schawlow had caused widespread interest in lasers
in the American scientific community. Researchers in labs around the
country raced to be first to construct a working model. The first
successful device appeared on July 7, 1960, built by a previously unknown
researcher who had worked totally on his own—Theodore H. Maiman of
the Hughes Aircraft Company in Malibu, California.

Maiman's laser was small (only a few inches long) and not very
complicated. The core of the device consisted of an artificial ruby about
one and a half inches long, so Maiman called his invention the
"ruby laser." The ruby acted as the lasing medium, which is
the substance that supplies the atoms or molecules to be stimulated. (In
Townes's maser, the medium had been ammonia gas.)

Maiman knew that the atoms inside the ruby would need to be excited
somehow. In the maser, the excitation method had been heat, but heating a
ruby would only cause it to break. Searching for an alternate method,
Maiman noted that light passes through a ruby, and he wondered if ordinary
light itself could be used as the excitation device. Maiman rigged a
powerful flash lamp so that it ran through a glass tube. The tube was bent
into the shape of a coil and wound several times around the ruby. When the
lamplight flashed, the photons excited the atoms in the ruby, and these
excited atoms became stimulated and gave off their own photons.

Maiman had accomplished the first step in the lasing process. He had
stimulated the atoms in the medium to produce photons. But to amplify the
light, he needed to increase greatly the number of photons being produced.
In the maser, amplification had occurred inside the resonant cavity where
the particles
bounced back and forth. In Maiman's laser the ruby itself acted as
the resonator because it contained the excited atoms. However, there was
nothing in the ruby for the photons to bounce off of. Furthermore, the
ruby was nearly transparent. The photons created would just pass through
and escape. Maiman had to figure out how to make the photons bounce back
and forth and also how to keep them from escaping. He accomplished both of
these goals in a very simple way: As the ruby was shaped like a cylinder
(something like a long soup can but much smaller), Maiman coated each end
of the ruby with silver. The ends then became mirrors pointing toward the
center of the ruby. Because the mirrors faced each other, the photons
bounced back and forth through the ruby over and over again.

The Ruby Laser

A ruby laser works much like a maser. But instead of microwaves, it
produces an intense beam of visible light. This occurs when the
molecules of an artificial ruby are "excited" by a flash
of ordinary light from a flash tube, which surrounds the ruby. The
"excited" ruby molecules begin to emit photons of visible
light. The photons reflect off of mirrors located at both ends of the
ruby. The reflected photons continue to excite more and more ruby
molecules, thus producing more and more photons. This production of
photons amplifies the light inside the ruby. The mirror on one end of
the ruby is only a partial, or half-silvered, mirror, so some of the
light passes through it. This light is the laser beam, or beam of
amplified light.

The next problem Maiman faced was how to allow his beam of amplified light
to get by the mirrors and escape. His solution was to make the coating of
silver on one end of the ruby very thin so that it became only a partial
mirror, reflecting some photons back into the ruby while allowing others
to escape. The ones that escaped became the actual laser beam. To
Maiman's delight, the beam of strange deep red light shot out of
the laser and registered on a nearby detector. As in the maser, the entire
process happened extremely fast—in only a few millionths of a
second.

A New Era Begins

Maiman immediately asked a scientific journal to publish the results of
his experiment. But the editors of the journal did not realize the
importance of the work and refused to publish the paper. So Maiman
approached the editors of a British journal,
Nature,
and they agreed to publish his three-hundred-word article. Not
surprisingly those few hundred words excited scientists all over the
world, and dozens of labs began to build their own laser devices,
initiating a new scientific era.

Researchers quickly realized that other materials besides the ruby could
be used as laser mediums. The first gas laser used a mixture of helium and
neon gases; and many other types of substances, including crystals, carbon
dioxide gas, vaporized metal, and even colored dyes, became laser mediums.
As more and different types of lasers were developed, scientists started
thinking of tasks for lasers to perform. People in communications,
industry, medical labs, and the military all rushed to find ways they
might benefit from the new type of light. Astronomers wanted to use lasers
to study the sun and stars; engineers wanted lasers to cut and weld metal
parts; doctors saw potential for lasers in performing eye operations and
burning away tumors; military leaders thought lasers might be developed
into death rays to shoot down enemy planes; and so forth.

The laser also promised to benefit its inventor with a great deal of
prestige and money. The problem was that several researchers had come up
with the idea at about the same time. This made it difficult for the U.S.
Patent Office to decide who the actual inventor was. As it turned out,
Townes and Schawlow received patents for the basic laser principle, and
Maiman received a patent for the ruby laser. However, because he had
applied so late, Gould did not receive a patent; so he took the case to
court. The legal battle dragged on for years.

Dr. Gordon Gould, who coined the term
laser
in the 1950s, fought for recognition as one of the device's
inventors.

Gould had even more to be upset about. In 1964 the famous Nobel Prize for
physics was awarded to the men who had created the original designs for
lasers. Three men shared the prize: Townes and the two Soviet scientists,
Basov and Prokhorov. Again, Gould had been left out; and again, he refused
to give up. Although he had to borrow large sums of money to continue the
legal fight, it eventually paid off. In 1977 and 1979 Gould received
patents for two small parts of the lasing process. Finally in 1988 the
patent office granted him the major patent he had applied for back in
1959. And so, along with Townes, Schawlow, Maiman, Basov, and Prokhorov,
Gould was at last recognized as one of the founding fathers of the laser.

User Contributions:

Alexander Graham Bell was a noted Scottish Inventor who was born in Scotland and educated in Scotland who emigrated to Canada and passed away in Canada. Yes some of his work was done in America just like Albert Einstein. Can you please amend.

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